The SF2 Soundforge Noise Reduction plug-in (direct x) is much better than others. I personally have a low tolerance for analog hiss. There are DL's I did-and deleted because they were beyond the range of what I can stand,beyond what I can fix. I built a set of very revealing speakers-meaning I hear the good stuff-and the flaws,so I want to enjoy the good stuff without a lot of crud.

Someone mentioned NR on the TAPE DECK???? Okay,a recording CAN be RECORDED in DOLBY B or C or no Dolby. To playback-you playback in the format in which it was ENCODED. You can not just push the Dolby C button on a deck and improve a recording that never had Dolby. Also-Dolby is more of a NOISE PREVENTION. it can not take away noise on the source,it does reduce the accumulation of hiss inherent in making another generation. A lot of analog tapers don't get what dolby is.

The IDEAL is to have an end result as close to how the original event sounded as possible. When the source material involves a multi-gen 30yr old analog originally done on second rate gear,it is pretty easy to improve it using GOOD NR techniques and probably some EQ. I really have no appreciation for the Audio-Vegan mindset that insists every flaw,mistake and shortcoming of the recording process has to be preserved-and yet some folks do butcher the job. The "damaged" recordings referred to above....who has the pre-processed version? Are you SURE it got NR effects and what you heard is not the effects of a badly recorded original,a bad transfer to digital? or just age?
Some recordings I have DO have some NR artifacts or other processing flaws-but were salvage jobs of a recording that was unuseable wreckage otherwise-would have joined a little stack of discs I burned before I realized how awful the sound was.